1. Field of the Invention
This invention relates to the field of automatic power transmissions and, in particular, to such transmissions having a countershaft connected to a power source through a clutch.
2. Description of the Prior Art
Automatic transmissions usually include a hydraulic torque converter or fluid coupling located between the engine and the gear arrangement. These devices require a large, continuously pressurized hydraulic system and operate at fairly low efficiency over a substantial portion of their operating range. A preferred automatic transmission would not require the torque converter or hydraulic coupling but would require only a small oil pump to pressurize a much smaller capacity hydraulic system for operating the clutches and servos that engage the several speed ratios.
It is necessary that an automatic transmission, particularly one for use in a vehicle whose engine and transmission are transversely mounted, require only a small space and that its overall dimension that extends in the transverse direction be as short as possible. Preferably, an automatic transmission would permit several aligned and coaxial input shafts to cooperate and in this way reduce the length that the transmission occupies between the drive wheels of the vehicle. The length of the transmission can be minimized if the number of gear wheels supported by the output shaft and by the countershaft is a minimum number of speed ratios that can be produced by the transmission. U.S. Pat. Nos. 2,599,801, 2,612,787, 2,654,261 and 2,644,340 describe multiple countershaft transmissions in which ratio changes are produced by friction clutches that are selectively engaged and disengaged in order to produce the gear ratios. These transmissions are particularly concerned with maintaining an uninterrupted flow of power from the engine to the output shaft of the transmission during speed ratio changes. U.S. Pat. No. 2,466,318 describes an automatic transmission having a single countershaft that supports gears fixed to the outer surface of the countershaft. One friction clutch connects the engine shaft to a pinion that drives the crankshaft in rotation; a second friction clutch joins the engine shaft to the output shaft of the transmission.